It's been a long time since I practiced law, but when you're invited to speak to lawyers from all over the world about climate change and potential court actions, you don't say no. So that's how I came to be at a lectern in Cape Town's prestigious International Conference Centre, presenting to lawyers not only from South Africa but also Nigeria, Australia, Canada, the United Kingdom, and many other nations, at the 18th Annual Commonwealth Law Conference.

I was one of a panel, which also included two environmental lawyers from South Africa, Catherine Warburton and Terry Winstanley, and a Professor of Law from Nigeria, Lanre Fagbothun. Terry spoke about water rights and said that the "capacity for growth" in any country is inevitably "impacted by quality and quantity of water". Professor Fagbothun spoke about land degradation and referred to the "strong desire for environmental justice".

The compelling topic, which I addressed, was Climate Justice. And although I had to accept at the start that many have tried, but none have yet succeeded in obtaining real redress from the Courts for the harm caused due to climate impacts, I also reminded delegates of what Martin Luther King once told us: "The arc of history is long, but it bends towards justice."

Even if politicians finally came to their senses tomorrow and created an international mechanism to immediately halt greenhouse gas rises, there was still going to be at least 50 years of climate impacts to be felt. And most of those are being experienced now, and will be in future, by the most vulnerable people in the world. Those impacts of course include higher temperatures and sea level rises, but also extreme weather, increased drought, changed ecosystems, and potentially ocean acidification.

Speaking in Cape Town, enabled me to point out that the South African government themselves says climate change is a threat to the sustainability of water supplies, and that South Africa is facing a water crisis in the coming decade. Yet their energy policy is based upon coal, and the coal fired power stations already use a shocking amount of water: 10,000 liters every second. For those, like me, who cannot imagine what that means, it's this: an Olympic sized swimming pool full every four minutes!

And of course there are severe economic implications too including the 10 to 28 billion dollar losses in America from Hurricane Sandy, and the more than 5 to 10% GDP losses estimated by the 2006 Stern Review. As Christine Lagarde (Managing Director of the IMF) has said: "Unless we take action on climate change, future generations will be roasted, toasted, fried and grilled".

There are already hundreds of cases being heard in the United States and elsewhere – some under local statutes, some under Environmental Impact Assessment legislation – and other ways in which people could access justice in years to come. Some courts are already acting to close older power plants or stop new ones. The day before I spoke, we'd heard from the United Nations High Commissioner for Human Rights, Justice Navi Pillay, and she reminded all of us about, how every person has the right to health and the right to life, how all human rights are interconnected, and how no-one should be deprived of them, whether by companies or by states. So I felt quite justified when I sent this warning to fossil fuel companies (and their lawyers) that one day those companies will be held to account for the humans who suffer terribly from their thirst for profits.

I had the experience of being accosted by two law partners from Nigeria who told me they were 'inspired to DO something' with the information they'd gotten from that session. That felt good. And as the week went on, other lawyers sought me out to ask for copies of the presentation – some teach law and wanted to add to their syllabus, others practice law and want to understand how to work for the potential victims of climate change or how to advise their corporate clients about the risks which are coming.

Later in the week, I was privileged to speak at a specially arranged seminar for LLM Students at the University of the Western Cape on the same topic. As this message goes out, that the time IS coming when fossil fuel companies will be held to account, I feel proud that Greenpeace is at the heart of it, and of not simply reporting the law, but often making it.